Cited Patent Reference 1, for example, has described an example of this kind of lens apparatus according to the related art. Specifically, the Cited Patent Reference 1 has described a linear actuator, an optical device and a lens-barrel for driving an image pickup lens in an image pickup apparatus such as a camera and a video camera. The lens-barrel described in this Cited Patent Reference 1 is characterized in that this lens-barrel uses a linear actuator in which a moving lens group movable in the optical axis direction, a lens holding means for holding the moving lens group and which can be freely slid along a guide in the optical axis direction, a drive means for driving this lens holding means and a position detecting means are provided at the four corners of the lens-barrel around the moving lens group in the optical axis directions.
According to the lens-barrel having the above-mentioned arrangement described in the Cited Patent Reference 1, there can be expected such effects in which while a bad influence exerted upon magnetism from a magnetic circuit can be decreased to the minimum, the lens-barrel can be reduced in size in the width direction by effectively using vacant spaces of the four corners of the lens-barrel and the lens-barrel can be made compact in size.
Cited Patent Reference 2, for example, has described other example of a lens apparatus according to the related art. Specifically, the Cited Patent Reference 2 has described a lens-barrel for use with a still camera and a video camera. The lens-barrel described in the Cited Patent Reference 2 is characterized in that it includes a movable lens-barrel with a lens held thereon movable in the optical axis direction and which includes a plurality of guide grooves parallel to the optical axis, a fixed lens-barrel having a plurality of second guide grooves opposing to the first guide grooves and which are parallel to the optical axis and a plurality of hard balls sandwiched between the opposing first and second guide grooves.
According to the lens-barrel having the above-mentioned arrangement described in the Cited Patent Reference 2, there can be expected such effects in which the hard balls are sandwiched between the guide grooves parallel to the optical axis so that the movable lens-barrel can be moved forward and backward very smoothly.
Cited Patent Reference 3 has described a further example of a lens apparatus according to the related art. Specifically, the Cited Patent Reference 3 has described a lens-barrel apparatus and a drive apparatus for driving a driven body which can be applied to a lens system of a video camera and the like. The lens-barrel apparatus described in the Cited Patent Reference 3 is characterized in that it includes a lens-barrel, a lens located within the lens-barrel, a holding means for holding the lens, the holding means including a coil, a yoke located within the lens-barrel in response to the circumference of the holding means, a magnet located within the yoke to move the holding means within the lens-barrel, the magnet constructing a linear actuator together with the coil when the coil is energized and a guide means for driving the linear actuator to guide the holding means of the lens along the lens-barrel, the guide means located at the position inside the radius direction as compared with the yoke, the magnet and the coil.
According to the lens-barrel apparatus having the above-mentioned arrangement described in the Cited Patent Reference 3, there can be achieved the effects in which the guide means such as a guide shaft need not be located at the outside of the lens-barrel apparatus so that the outer shape of the lens-barrel apparatus can be simplified.
[Cited Patent Reference 1]: Japanese Published Patent Application No. 11-150972
[Cited Patent Reference 2]: Japanese Published Patent Application No. 8-29656
[Cited Patent Reference 3]: Japanese Published Patent Application No. 8-15593
However, in the related-art lens apparatus using the linear actuator as the driving means, as shown in the Cited Patent Reference 1, it has been customary for most of the lens apparatus to hold the lens hold frame by using the guide shaft. For this reason, it has been customary that the coil of the driving means is fixed to the place of one portion distant from the center of the optical axis of the movable lens holding frame with a constant distance. Also, it has been customary that the permanent magnet and the yoke of the driving means are located so as to pass through the coil or they are located distant from the coil with a constant distance, that is, the permanent and the yoke are of the so-called coil moving system.
On the other hand, although there is a magnet moving system for moving the permanent magnet and the yoke while the coil is being fixed, the place in which the magnet moving system is located is the same as that in which the coil moving system is located. In such case, it is unavoidable that a part of the lens-barrel is projected or that the outer shape of the lens-barrel becomes angular. As a consequence, a part of the lens-barrel is unavoidably increased in thickness and hence it has been difficult to make the lens-barrel become cylinder with a small diameter, thereby making it difficult to miniaturize the whole of the image pickup apparatus. Further, since most of the lens-barrel uses a ring-like coil having a rectangular shape as a coil and the effective portion of the ring-like coil as the magnetic circuit is only one side of the rectangular, it is inevitable that a magnetic loss becomes large from a standpoint of circuit efficiency of the magnetic circuit.
Also, while some related-art lens apparatus had a ring-like coil located at the outer peripheral side of the lens, such related-art lens apparatus had a structure in which a yoke is formed of a different member, the yoke being inserted into the lens-barrel. As a result, the lens-barrel was increased in thickness, the whole of the apparatus was increased in size unavoidably and driving efficiency was not satisfactory.
On the other hand, a related-art collapsible type lens apparatus will be considered. It has been customary for a collapsible type lens apparatus that a lens holding frame with a cam pin restricted by a linearly movable lens-barrel rotates a cam ring with a cam groove to allow the cam pin to trace the cam groove, thereby the linearly movable lens-barrel to be collapsed. In this case, since frictional resistance generated when the linearly movable lens-barrel is slidably moved is extremely large, it has been customary that the collapsible type lens apparatus can be collapsed by using a DC motor which generates large torque, reduction torque increased by a gear arrangement or by manual operations. Accordingly, it has been difficult to collapse the collapsible type lens apparatus by a linear motor. Furthermore, when the collapsible type lens apparatus is provided with the gear arrangement or motors are separately mounted on the collapsible type lens apparatus, it is unavoidable that the outer shape of the lens-barrel of the lens is increased in thickness. As a result, the whole of the collapsible type lens apparatus might not be miniaturized and decreased in diameter as one wants it to be.
The problems which the present invention will solve and with which the related-art lens apparatus encountered will be described below. In the lens apparatus according to the related art, it has been difficult to miniaturize the lens-barrel of the lens while a plurality of lens holding frames is being made movable. In order to reliably move the movable lens-barrel forward and backward, it is necessary to increase an output from a drive mechanism. To this end, it is unavoidable that the whole of the lens apparatus becomes large in size. In particular, when movable lens-barrels are provided at the inside and the outside of a fixed lens-barrel so that a plurality of movable lens-barrels can be moved forward and backward, the lens apparatus is increased in length in the optical axis direction or it is increased in length in the direction perpendicular to the optical axis direction. Therefore, it was difficult to miniaturize the whole of the lens apparatus.